1. Field of the Invention
This invention relates to a process for the production of sclareolide from sclareol and/or abienol.
A full definition of the trivial names and abbreviations used in the following in conjunction with the accompanying numbers in round brackets is given in the Example section which shows the associated IUPAC name and the corresponding structural formula.
2. Statement of the Related Art
Ambroxan (7) is a valuable ambergris fragrance which is found in a metabolic secretion of the sperm whale (cf. Ullmanns Enzyklopadie der technischen Chemic, Vol. 20, pages 283, Weinheim 1981). In view of limited natural resources, the increasing demand for ambroxan has led in recent years to the development of processes by which ambroxan can be synthetically obtained from inexpensive raw materials. Sclareolide (6) in particular has proved to be an important ambroxan precursor so that the concern of many research groups has been to develop processes by which sclareolide can be synthesized from natural raw materials, more particularly sclareol (1).
According to U.S. Pat. No. 3,050,532, sclareol is first oxidized with potassium permanganate under alkaline reaction conditions to form the hydroxyketone (3) which, without further isolation, is converted with glacial acetic acid into the enolethers (4). The enolether is then oxidized either with potassium permanganate or with chromic acid. The oxidation product obtained is saponified and then cyclized to form sclareolide (6). Unfortunately, this process is attended by the disadvantage that the oxidation step is carried out with potassium permanganate which is ecologically unsafe, i.e. toxic. In addition, the MnO.sub.2 (magnesium dioxide) formed therefrom is very difficult to filter off in the working-up phase.
Finally, German patent application DE 39 42 358 describes a process in which sclareol is first oxidatively degraded with hypochlorite salts in the presence of ruthenium salts to form the hydroxyketone (3) and/or the enolether (4), the intermediate product thus obtained and isolated is oxidized with peracids and/or peracid salts and, after saponification and acidic ring closure, is converted into sclareolide. This process gives sclareolide in a yield of around 65%, based on sclareol.
Accordingly, in view of the key position of ambroxan in the field of fragrances, there is a general need to develop improved syntheses. This demand extends in particular to improvements in individual process steps and to the development of alternative syntheses for the production of important intermediate products or precursors of ambroxan. Accordingly, the problem addressed by the present invention was to create better access to sclareolide starting out from sclareol and structurally closely related compounds.